Tr. Meling et J. Odegaard, THE EFFECT OF SHORT-TERM TEMPERATURE-CHANGES ON THE MECHANICAL-PROPERTIES OF RECTANGULAR NICKEL-TITANIUM ARCHWIRES TESTED IN TORSION, The Angle orthodontist, 68(4), 1998, pp. 369-376
Due to their exceptional temperature sensitivity, superelastic nickel
titanium wires may be affected by temperature changes associated with
ingestion of cold or hot food. It has been assumed that the alteration
s in archwire stiffness associated with short-term cooling or heating
are transient. This investigation studied the effect of these temperat
ure changes on the torsional stiffness of nickel titanium alloys. Eigh
t rectangular superelastic wires were activated to 20 degrees, in long
itudinal torsion at body temperature and subjected to cold (10 degrees
C) or hot (80 degrees C) water with the strain held constant. The tor
sional stiffness of some wires was strongly affected. The effect of ho
t water disappeared quickly, but the wires remained at a level of redu
ced torsional stiffness (up to 85% less than baseline) after short app
lications of cold water. The most thermodynamic archwires showed incre
mental reductions in torsional stiffness when cold water was repeatedl
y applied. Furthermore, the torsional stiffness remained low (up to 50
% less than baseline) and showed no tendency to increase even after 2
hours of postexposure restitution. It is conceivable that some wires m
ay provide inadequate forces for tooth movement after ingestion of col
d liquids.